PurposeThis study aims to predict ethical self-identity’s effect on consumer buying behavior of biodegradable bags. Moreover, a moderated mediation model is tested by analyzing the mediating role of attitude and the moderating role of religiosity to investigate buying behavior. Few studies have been conducted to explore moderated mediation to predict consumer behavior based on belief congruence and planned behavior theories, according to previous literature, indicating a literature gap in consumer behavior studies. Accordingly, the moderating role of religiosity in the relationship between ethical self-identity and purchase intention in the context of biodegradable bags was used to contribute to the consumer behavior literature.Design/methodology/approachThe population of the study included literate consumers who are aware of biodegradable bags and keen to buy them. The data were collected from consumers of twin cities (Rawalpindi/Islamabad) via purposive sampling. The data were collected from 310 consumers five-time lags.FindingsThe findings suggest that ethical self-identity influences the buying behavior of consumers toward biodegradable bags. In this study, the theory of planned behavior provides greater implications to predict consumer buying behavior because the subjective norm, perceived behavioral control and attitude were found to have a significant influence on purchase intention, which further predicts the actual consumer behavior.Research limitations/implicationsThe study’s sample was limited to one geographical area and the sample was limited to only biodegradable bags. Future studies may go for a cross-comparison of industries or multiple environment-friendly products to enhance the generalizability of the research.Practical implicationsThis study provides useful insights to the companies of consumer-based brands to use eco-friendly practices from production to packaging and consumption. Environment-friendly consumers are ready to pay a premium price for environment-friendly products, which encourages decision-makers companies to cater to this niche market. Moreover, companies can focus on factors that influence their decision-making, such as ethical and moral values of responsibility, while planning their advertising strategies. Furthermore, the positioning of the environmental or consumer personal care products should be done by considering the personal disposition factors because they reinforce the actual behavior of employees.Social implicationsFor researchers, this research opens new avenues for predicting consumers’ buying behavior by applying the theory of planned behavior in the plastic bag industry. This study provides useful insights to the companies of consumer-based brands to use eco-friendly practices from production to packaging and consumption.Originality/valueThe proclivity to buy biodegradable bags increased over time, providing opportunities to the companies to offer environmentally friendly products to an increasing number of customers. However, personal deposition factors, such as religiosity and consumer views, are less well understood in terms of predicting actual behavior. Few studies have been conducted to explore moderated mediation to predict consumer behavior based on belief congruence and planned behavior theories, according to previous literature, indicating a literature gap in consumer behavior studies.